Why lemurs get sick: A lesson for humans, too

Female blue-eyed lemur

What lessons can humans learn from our far distant prosimian primate cousins about living well and eating a healthy diet?

This was the question on my mind as I toured the Duke Lemur Center in Durham, North Carolina with colleagues attending Science Writers 2012. (Read Christie Wilcox’s full report about our tour over at Science Sushi on Scientific American.)

When I learned on the tour that lemurs were getting sick, I inquired further from our tour guides, education associate Chris Smith and education manager Niki Barnett. The thought of these adorable creatures—somehow related to me because of a common ancestor some 50 to 80 million years ago—suffering from the same types of chronic diseases as modern-day humans encouraged me to want to find out more about their care and treatment.

Lucky for me, Chris, who might’ve tired from me badgering with so many questions, helped me arrange an interview with the center’s senior veterinarian. On my second visit to the center at a later date, Dr. Cathy Williams described for me, and showed me, what it was like to work as a clinician in the world of lemurs.

Lemurs and humans, not so different

There are multiple parallels between why humans get sick and why the lemurs do, Dr. Williams told me.

"They mainly have to do with diet," she said. The diets for lemurs at the center are not necessarily ideal—even in this magical place, home to the largest population of the world's most endangered primates outside of Madagascar.

Routine physical exams and dental cleanings make up most of a day in the life of a senior veterinarian, Dr. Williams told me. The veterinarians and keepers work hard to make life for the lemurs as healthy and comfortable as possible.

Sifakas eat primarily leaves

I was interested to find out that captive lemurs often get a lot of tartar build-up on their teeth while wild lemurs do not. The reason is mainly because the diets of captive lemurs are mainly composed foods that are often much higher in sugars and starches than in Madagascar.

"There is less fiber, the fruits are softer, and there’s less chewing and pulling leaves from trees," Dr. Williams said. Chewing and pulling in the wild act as nature’s way of brushing and flossing, Dr. Williams said, "We see a lot of gum diseases. I’ve never seen that in the wild at all." 

Dental care

Lemurs in the center receive dental cleanings every couple of years. If one of the animals has dental problems, they get cleanings more often. Dr. Williams also encourages behavioral trainers to regularly floss the teeth of the lemurs, time and human-power permitting.  

Similar to lemurs, dental caries are somewhat of a novelty among humans, according to Randolph Nesse and George Williams. The authors of Why We Get Sick: The New Science of Darwinian Medicine wrote that tooth decay and cavities only became more common because of today’s frequent and prolonged exposure to starches and sugars that feed the bacteria responsible for producing acid that causes demineralization of teeth.

Caries exist in alongside a long list of chronic health-related problems caused by "modern dietary inadequacies and nutritional excess," Nesse and Williams write. Others we're all familiar with are obesity and diabetes.

Choosing appropriate foods

Blue-eyed lemurs and sifaka play together, but have different diets.

When I asked Dr. Williams if obesity was a growing problem among captive lemurs, she said that it was, although not so much at the center.

Because the center is in the habit of loaning animals out to other zoos around the country, they've seen obesity become a problem in part because of the difficulty in training zookeepers on how to appropriately feed the lemurs appropriately.

The major challenge, she said, is in simply educating keepers to understand that feeding strategies are different for different species of lemur. All lemurs are similar in that they are herbivorous hindgut fermenters having simple stomachs and large cecums (as opposed to foregut fermenters, which are generally ruminant species like cows); however, intestinal transit times between lemurs vary greatly.

On one end of the spectrum, you have the red-ruffed lemur. In this species, the intestinal transit time is short, so fermentation in the cecum is bypassed. Their feeding strategy is to eat easily digestible foods, and a lot of them. They primarily eat a lot of fruits, but don't absorb a lot when they do. "The joke goes: it goes in a banana, it comes out a banana," Dr. Williams said.

On the other side of the spectrum, there are bamboo lemurs and sifakas with long intestinal transit times. These lemurs eat primarily leaves and rely on their fermentation for production of short-chain fatty acids to supply the majority of their energy (similar to gorillas versus chimps). In comparison, the ring-tailed, brown and blue-eyed lemurs tend to be more generalist in eating a variety of leaves, fruits, and some insects. Ring-tailed lemurs may even make a meal out of a small bird on occasion.

Many of the problems result from insufficient knowledge or misunderstanding on the part of zookeepers. If a red-ruffed lemur is put on a diet of leaves, the animal won't absorb enough nutrients to survive for very long. Conversely, if a sifaka is fed a diet high in fruit, the diet will favor growth of microflora that uses starch more efficiently and doesn't ferment fibers well; the resulting changes in pH alone will give the animal diarrhea until its probable death.

To prevent sickness and death of animals that are on loan, Dr. Williams said zookeepers are now required to come to the center to be trained, "They'll learn that, yes, sifakas like banana, but, no, we can't feed it to them. Yes, they will eat it, but it's not good for them."

Controlling portions and low-glycemic foods

Ringtailed eat a mix of fruits, leaves, insects, and even birds.

Earlier this year, it was at one of these Prosimian Husbandry Workshops where Dr. Williams shared new information with zookeepers on what feeding strategies in the center have been used to help prevent or control obesity and diabetes.

One important bit of knowledge Dr. Williams passes on is that "when we say 'frugivore,' we're talking about a wild diet that is very high in fiber, low in starches. But when folks think 'frugivore' in captivity, they think apples, bananas, and grapes—these are not at all like fruits in the wild."

Lemurs at the center are never overfed, Dr. Williams told me, but diabetes is still a significant issue. "The diabetics in our colony were never obese, but we're still causing problems that lead to insulin resistance," she said. In addition, kidney failure and cancer are other main causes of death.

Much in the same way humans might like "marshmallows and chocolate eclairs," as Nesse and Williams write in their book, the problem with lemurs is that they have "mismatch of tastes evolved for stone age conditions."

All lemurs enjoy the types of fruits and starchy vegetables we've cultivated for our taste buds, Dr. Williams said, which can easily lead to overfeeding with these kinds of foods and that can lead to obesity and diabetes.

Lemur care, age, and inflammation

Once an animal has diabetes, it must be controlled with a low-glycemic diet—consisting of leaves and primate biscuits that are higher in fiber, lower in starch and sugar—alongside anti-diabetic medications such as metformin.

                                                                                                                      

I asked Dr. Williams how the lemurs responded to being put on their low-glycemic biscuits versus their normal, more palatable, sugary, cookie-like treats. She said they responded in the same way as a human would after hearing, "OK, you're not eating anything but bran and leafy greens for now on." Not very well at all.

Why can't I play outside?

There are several contributing factors to chronic disease in lemurs, Dr. Williams said. One may be simply be age, since the animals at the center, depending on the species, can usually live well into their 20s and 30s, which is not normal in the wild.

These older animals also have limited mobility, resulting from age-related wear and tear, and are not able to enjoy some of the free-range enclosures the lemur center provides. A more sedentary lifestyle indoors can lead to less insulin sensitivity and, while the center does offer enrichment programs to encourage activity, Dr. Williams notes, the rewards used in these programs is usually sweet treats.

Seeking the ideal lemur diet

                                                                                           

How these aging lemurs are fed and what they're fed in their diets are still not what Dr. Williams would consider ideal. "It could be better," she said; for instance, the lemurs usually receive all their food in one or two feedings daily while, in the wild, they generally graze throughout the day. More feedings over the course of the day may help stabilize blood sugar.

In addition, Dr. Williams has noted mild, low-grade inflammation is a factor. As part of her clinical duties, she performs autopsies whenever a lemur dies. Histopathological exams of tissues upon death often reveal a mild chronic colitis or hepatitis. "We don’t know what the cause is," Dr. Williams told me.

 

One possible contributing factor, Dr. Williams told me, may be in the type of ingredients used in the flavored primate biscuits or other foodstuffs the lemurs eat. The biscuits are primarily grain-based, she said, containing corn, soy, or wheat to provide one source of starch, soluble fiber, and insoluble fiber, along with protein sources.

Ideally, she said, a lemur's diet should consist of diverse types of fiber found in the same types of wild fruits and vegetables found on Madagascar. These could include several types of pectins, gums, and other fermentable fibers. Another area of concern may be omega-6 to omega-3 ratio of the lemurs' chow.

Education outreach and lemur nutrition research 

Dr. Williams 

A major challenge is in the need of further nutritional research in primates as a whole and, more specifically, with lemurs. Then, afterward, educational outreach.

After my interview with Dr. Williams, I contacted Michael Schlegel, Ph.D., director of nutritional services for the Zoological Society of San Diego to discuss her recommendations. Dr. Schlegel's role is to formulate meals for all the animals in at the San Diego Zoo and supervise how they are fed.

Dr. Schlegel found Dr. Williams's findings highly interesting, saying, "We're always looking for new research and we do balance diets so that fruit is only a component. They do get vegetables, but we know more is what's good for them."

Zoo keepers and zoo nutritionists like Dr. Schlegel rely on guidelines given by the National Research Council's Nutrient Requirements of Nonhuman Primates, much as Americans rely on Institute of Medicine for dietary guidelines.

"We look at publications, and adjust to individual needs. We try to base diets on animal energy and metabolic requirements," he said.

Schlegel agreed that current dietary requirements for all primates are based on limited studies. Further research is needed in areas such as analysis of dietary composition of wild diets as well as controlled trials with lemurs as a species.

As it stands, the science of nutrition and diet is still young for humans and lemurs alike, but so far the similarities on how the modern world affects human health and how captivity affects our far distant cousins are striking.